Our main objective is to study the sequence of events and specificity in the formation of nerve-muscle and intraneuronal synapses in low-sensory cell cultures of embryonic muscle, spinal cord and sensory ganglia, placed in various combinations. Simultaneous microelectrode (recording, stimulating and iontophoresic) and time-lapse cinematographic techniques will be correlated with autoradiographic and electron-microscopic findings. Attempts to separate specific cell types by microdissection, velocity sedimentation and affinity columns in order to obtain "pure" cultures containing only one presynaptic and one postsynaptic cell type will be made. Long-term changes in synaptic efficacy and trophic interactions between synaptically connected cells will be examined. In addition, we will study the development of postsynaptic chemosensitivity, the regulation of chemoreceptor distribution and the role of postsynaptic receptors in synapse formation. BIBLIOGRAPHIC REFERENCES: Dichter, M. and Fischbach, G.D. (1977): The ionic basis of the action potential of chick sensory ganglion cells grown in cell culture. J. Physiol., in press. Cohen, S.A. and Fischbach, G.D. (1977): Relative peaks of ACh sensitivity at identified nerve-muscle synapses in spinal cord-muscle co-cultures Devel. Biol., in press.